docs: def add_event_callback(self, event_groups, callback):
          """Register callback for a group of timeline events."""
          if not event_groups:
              return False
  
          if not isinstance(event_groups, (tuple, list)):
              event_groups = [event_groups]
  
          for event_group in event_groups:
              if event_group not in TIMELINE.ALL_EVENT_GROUPS:
                  raise AbodeException(ERROR.EVENT_GROUP_INVALID,
                                       TIMELINE.ALL_EVENT_GROUPS)
  
              _LOGGER.debug("Subscribing to event group: %s", event_group)
  
              self._event_callbacks[event_group].append((callback))
  
          return True